A technique of the present invention is useful as a mechanical seal for sealing a fluid to be sealed in semiconductor production facilities, etc. In semiconductor production facilities, etc., when an impurity is included in a sealed fluid, it adversely affects the products. Therefore, it is necessary to prevent incorporation of an abrasion powder to the sealed fluid caused by wear of a seal ring at the time of rotation in the mechanical seal device. As a countermeasure, a non-contact mechanical seal device is used to prevent wear of seal surfaces of the seal ring.
As such a non-contact mechanical seal device, there is known a device comprising a rotational seal ring connected to a rotational shaft of a semiconductor production facility, etc. and having a rotational seal surface and a stationary seal ring having a stationary seal surface facing to the rotational seal surface of the rotational seal ring; wherein grooves (pockets) capable of connecting to a fluid supply path for supplying a pressure fluid is formed on the stationary seal surface (for example, refer to the patent articles 1 and 2).
Also, there is known a device wherein arc-shaped grooves are formed on the stationary seal surface and arc-shaped grooves are formed on the rotational seal surface of the rotational seal ring (for example, refer to the patent article 3).
In the above mechanical seal devices, a floating force of the stationary seal ring is made larger comparing with that of the rotational seal ring by forming grooves on the stationary seal surface, so that wear is prevented. Also, in such a mechanical seal device, a larger floating force can be obtained by increasing a volume of the grooves formed on the stationary seal surface.
However, as the volume of the grooves formed on the stationary seal surface increases, vibration arises in a behavior of the rotational seal ring. The vibration is a phenomenon called Pneumatic Hammer caused by compressibility of a pressure fluid supplied between the rotational seal surface and the stationary seal surface. On the other hand, when the volume of the grooves formed on the stationary seal surface is decreased to suppress the Pneumatic Hammer phenomenon, a sufficient floating force cannot be obtained and the rotational seal surface contacts with the stationary seal surface.
Also, in the above mechanical seal device described in the patent article 3, the grooves formed on the stationary seal surface and the grooves formed on the rotational seal surface have approximately the same size. Therefore, there is almost no volume difference and the effect of the grooves formed on the rotational seal surface cannot be obtained sufficiently, so that vibration also arises in a behavior of the rotational seal ring due to the Pneumatic Hammer phenomenon in this case.    Patent Article 1: Specification of the International Publication No. WO 00/075540    Patent Article 2: The Japanese Unexamined Patent Publication No. H03-277874    Patent Article 3: Specification of the U.S. Pat. No. 3,917,289